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merc 305 v8 1999 no compression

J

jansteam40

Contributing Member
hi guys i have a merc v8 305 5 ltr it has no compression at all on two cylinders , i have pulled the heads and all seems fine with the valves etc i then thought it was rings or piston so i have pulled the piston and that all seems fine any sugestions thanks:mad:
 
If the two low cylinders are next to each other, this usually indicates a blown head gasket between the two.
Bert
 
Parts Listing

you have a carb ? I looked at this site they don't have it. I don't think it matters one way or the other carb or efi. for the valve.

I know you can get them cheaper. but look up the number then do the search for cheaper or maybe someone here has them laying around.
 
bring the head (s) in question to a reputable automotive machine shop that works on or specializes on american engines. It is a standard chevy valve/head/all head components
 
RockAuto Parts Catalog big difference in price like 50 bucks difference. Rock 5 bucks the other link 55 bucks.

Hell for the price you can have the whole set 16 in all for almost one from the other site, just something to consider.

One other thing all the pushrods are straight nothing else went, rocker arm stud pull up a little maybe, on those 2.
 
cheifalen is this the actual valve i need because like you say this seems dirt cheap and is the number a manufacturers number or a rock auto parts number the merc number for this vv is 802555 and thanks for all the help
 
cheifalen i just realised this vv is the exhaust vv i need the inlet vv , i can get the exhaust vv over here but having a nightmare getting the inlet vv thanks again
 
Is this a new problem, i.e., did it ever run OK for you? One has to consider why the valve died as it may be a symptom of other issues and not causal.
 
i had an overheating problem which has caused this valve issue , i have cured the overheat problem and i have inspected all the other parts having taken the engine out this is the last thing on a long list just need that valve to complete the rebuild
the engine ran fine before all these issues
many thanks
 
From my MERCURY parts cd

Intake valve part number is 802555 5.0 litre 1999 5.0 litre

Could not find a automotive cross reference yet.
 
thanks kghost i have that merc number but over here in the uk they want about $150 just for one valve i have a part number from rockautoparts which is IV3104A as per the above link but before i order i just want to make sure it is the right part
many thanks for all your help once again
 
kghost another thing that you may be able to help me with seeing you are a senior member of this fantastic forum is marineeng used to send me emails of these posts but i dont seem to get them anymore am i doing something wrong or am i just stupid
 
I do not know all the working of this site, sorry.

As far as the valve goes what would help is the valve specs.

DIA.
LENGTH.

I was looking at a aftermarket web site and they have MANLEY valves for stock GM 5.0 litre as low as $10.00 US.

Valve, Intake, Stainless Steel, 1.940 in. Diameter, .341 in. Stem, 4.911 in. Length,

seems to be the standard spec.

If you can measure yours and it matches then it will make it easier to find.

Also why not go to a automotive machine shop and speak to them.

They probably have these in stock!!! Of course that is a big assumsion!!!
 
the spec of my valve is head dia 1.84 inches , the stem size is .341 the valve length is 4.879 it has one groove for the collets which is .260 from the end ,
 
YEs they did show valves of that size.

There were more valve available of the numbers I showed so I assumed it may be yours.

I think you are on the right path now.

You have the specs for the valve so you "should" be able to find a inexpensive replacement hopefully easily!!

GOOD LUCK!
 
re: "i had an overheating problem which has caused this valve issue"
Well I don't have the experience that many other members of this forum have with a large number of engines, however, the typical overheat related failure victims/results are (in order of occurrence insofar as I've seen) are:
1) Blown head gasket
2) warped head
3) cracked head
4) cracked block.

From my experience, bad valves happen:
1) Engine over propped
2)engine run at WOT for long periods of time
3) lifter failure/mis-adjustment (valve does not close/seat fully)
4) piece of carbon breaks loose and does not allow valve to close fully


Then again, just because I've never seen this particular failure chain, (overheat > valve failure) does not mean it can't happen, but I would think that an intermediate, undetected mishap, i.e., something in the lifter chain bound up when the engine got too hot happened...which sort of gets us back to #3 or #4 above.
 
the marine mafia does it on purpose. They jack a 5 dollar part up to 50-60 dollars.

These are standard valves just 1 year difference throw off the part number.

Threw out the rock auto site, but you have whitney and many others.

I can't really at this time track it down for you.

Ghost is better then me at the parts.

Take your time save money and research the one you need, should not cost more then 10 bucks american, plus shipping for each one.
 
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